Mode of testing railway rails on contact weariness

FIELD: the invention refers to the field of quality control of materials and manufacture goods for assessment of resistibility of rails to destruction due to contact weariness.

SUBSTANCE: contact weariness is induced by high-frequency dynamic components of interaction of wheels and rails, which become apparent at moving at high speed. The mode of testing railway rails on contact weariness is in that tested samples of rail steel are rolled by pinch rolls in longitudinal direction until appearance on the surface of the sample of dents and also deep indents. As samples test rails are used. The diameter of a pinch roll is chosen under condition of equality of reduction ratio of linear size of the site of contact of the pinch roll with the rail along the axis of the last in comparison with corresponding size responsible to conditions of exploitation and speed reduction ratio of rolling motion of the pinch roll along exploited rail.

EFFECT: the invention allows to increase reliability of test rails' control at danger of resulting defects from contact weariness caused by contribution of high frequency components in dynamic interaction of wheels and rails which becomes apparent at the moving of trains at high speed.

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The invention relates to the field of quality control of materials and products and can be applied in relaitvely centers and laboratories at leading metallurgical enterprises producing rails, or on an experimental basis the relevant units of research institutes and universities transport profile to evaluate the resistance rail contact fatigue fracture caused by high-frequency dynamic components of the interaction between wheel and rail, which are manifested in a significant (120-160 km/h or more) speeds.

There is a method of assessing fatigue strength of rail steel [1], which allows in a laboratory setup to reproduce contact damage to the rails, resulting in operating conditions. The principle which is the basis of a constructive embodiment of the method consists in the following. Imitation of force, which is in operation the material in the surface area of the rail head, is implemented by the rolling of the pressure rollers on the subject roller-standard; at this pressure rollers are made in two configurations (with conical and rectangular profile in cross section). Rolling of the first roller on the sample forms the active site of plastic deformation. Next to the first, the second pressure roller does not allow the strain to develop in the direction of the surface is skating sample, shifts the metal again to the edge mates with the conical surface of the first pressure roller and forms therein influx. Between the influx and the side face of the specimen the crack fatigue, growing at an angle to the plane of the ski of the sample. This type of defect, according to the authors [1], similar to the defect 11, found on the rails in the straight sections of the path. Upon further testing of the test wheel in the gorge under the action of normal and tangential forces appear damaged. These injuries represent evolving in time chipping in the field of large plastic deformation. This type of defect (also according to [1]) is similar to the defect 11.2 resistant filament curves of small radii.

The known method, which has disadvantages as the method of play of the defect, and by contact endurance steel rail, raises a number of objections. First of all, the distribution of the contact stresses in the roller-sample will differ from the distribution of stresses, meeting performance conditions.

In addition, the cutting of the test clip leads to the fact that testing is not the surface layer of metal which is active in track and trials are layers lying at different depths under the surface of the ski. In the load torque line which begins rolling is with the direction of the acting forces corners, distributed in the range from 0 to 90° that do not match the real conditions of operation.

To achieve compliance with the laboratory test results to the behavior of the material in track conditions, it is necessary to bring the method of loading samples to the nature of the loading rails in the track. In addition, the test should ensure the allocation of the contribution of high-frequency components of the dynamic interaction between wheel and rail. Test rails on the experimental ring, the best possible approximation to the travel conditions, does not solve this issue not only due to the significant material and energy costs, but also in technical terms - because of the impossibility of allocating impact factor a high frequency amongst the harmful effects of dynamic components.

Closest to the claimed method [2], in which samples cut from the rail head in the longitudinal direction, laid on the perimeter of the disk. They obkatyvalisj pressure rollers, which allows to simulate the work of rails resistant threads in a curved section of road. Criteria for comparative evaluation of resistance of rails to the formation of defects contact fatigue is the appearance of fishermen and development of their deep indentation depth, as per. As shown by the test specimens made from the head of the rail 65, the defect 11.2 reproducibility is camping for 70 hours (after a 5.5· 10⁵of loading cycles), which is hundreds of times smaller than the time of occurrence of the first signs of defects on the rails in operation.

Along with the advantages of this method is the prototype has a disadvantage. Fillet sample of steel from rail head is actually broken likeness in the correspondence of the dynamics of the stress-strain state of the material in the sample real conditions change this state when exposed to the wheels of the rolling stock on the track. This difference becomes particularly significant at high speeds. As the trend towards higher speeds (up to 140 km/h and more) on the number of routes currently stored, the inability to satisfy discussion of the way the similarity in terms of reproducibility of the contribution of high-frequency components of the mechanical action of the wheel on the rail, significantly reduces the value of the method.

It should be noted that the wheel rolling on the rail at high speed can be interpreted from the position casiodoro interaction [3-5]. Such speed significantly transform the spectral composition of the force action of the wheel on the rail head and change the working conditions of the material. The activity of the process will be determined by the contribution of wave interference process and a significant increase in the number of loading cycles, and petyaev material, at comparable magnitudes in the time of action of dynamic loads on the contact area with the time at which the wave crosses twice the height of the rail. This casts doubt on the quasi-static approach to the problem and gives the basis to search for resonances that define the development of the system of internal defects, due to the establishment of alternating stress cycle, which is accompanied by intense energy dissipation. In fact, the method of [2] would be far from the realization of such a possibility, but when it is used instead of a full-scale rail was sampled from a smaller cross-section cut from the head rail, which led to the mode of loading rail steel, non-operational.

The objective of the invention is to increase the reliability of control experienced rails on the risk of contact fatigue defects caused by the contribution of high-frequency components in the dynamic interaction of wheel and rail, which manifests itself at high speeds of the motion.

The essence of the invention lies in the fact that the samples pass around the pressure rollers in the longitudinal direction until the surface of the sample fishermen, as well as a deep indentation depth, as per, at the same time as the samples used by the experienced rails, and the diameter of the pressure roller wybir the Ute from the condition of equality of the reduction ratio of the linear size of the area of contact of the roller with a rail on the axis of the latter in comparison with the corresponding size, meeting performance conditions, and the reduction ratio of the speed of rolling of the roller relative to the speed of the wheel rolling on the rail in operation.

Imitation casiodoro impact on the rail can be carried out in laboratory conditions at a much lower speed rolling wheels compared with field conditions, if you satisfy the following ratio: reduction ratio rolling velocity is equal to the reduction ratio of the contact patch of the wheel and rail. In accordance with the concepts described in [6, 7], we can assume that the contour of the elastic contact of railway wheel and rail head has the shape of an ellipse. The maximum compressive stress that develops in the center of the ellipse, is

Here P is the power of squeezing two cylinders, a S is the area of an ellipse is equal to π ab, where a is the semimajor axis of the ellipse, b is the semiminor axis of the ellipse.

The values of a and b can be determined by the formula

Here ν is the Poisson's ratio, E is the modulus of elasticity;

if R>r

when r>R, (see [6])

where R is the radius of the wheel rolling circle, r is the radius of the running surface of the rail head. The values of m and n are found from the table at a known angle θ to the which is determined from the condition

Adopted this notation, the transition from the case of R>r (characteristic ratio of the radii of curvature of the surfaces of the riding wheel and the rail head in the natural environment) to the case of r>R (responsible model variant) as axis pads, coinciding in direction with the axis of the rail, instead of the parameter and use the b parameter. In the end, if we write the expression (2) twice: for in the aimogasta of wheel and rail in situ, operating conditions by marking the corresponding options indexes “n”and for the interaction between wheel and rail in model conditions, using in this case, the index “m” - it is easy to get the value

We can rewrite (3) so that the right side was only known values (the values of which are set when the implementation of the method),

the value of a_n/b_mthat represents a reduction ratio of the linear size of the area of contact of the roller with a rail on the axis of the latter compared with the corresponding size of contact area wagon wheel-rail (i.e. the appropriate size, complying with operating conditions), equate the value of ν /ν_m- the reduction ratio of the speed of rolling of the roller relative to the speed of the wheel rolling on the rail during operation (ν - the speed of the rolling wheel, ν_m- the speed of rolling of the pressure roller).

The tests simulated operational speed ν =120 km/h, the speed of rolling of the pressure roller (defined structural features of the stand) is set equal to ν_m=4 m/S. Thus, relate ν /ν_m=33,3(3)/4=8,3(3)=a_n/b_m(this value represents cu is tnost reduce the speed of rolling of the roller relative to the speed of the wheel rolling on the rail in operation). Under given load on the pressure roller P_m=4 kN, which is less than the dynamic load P_nwheel of empty freight car about 30 times (take R_n≈120 kN), and the same radii of the heads of experienced rail and rail operation r≈ 0.3 m (to simplify the example as a sample of experienced rail with proven head), from (4) it is possible to find the radius R_mand the diameter D_mthe pressure roller.

Combination of parameters is presented in the left part (4), denoted by S. the Value of m_Nincluded in the right part of (4), found in the table on page 4 (the radius of the wagon wheels R_n=value (0.475) m): m_n≈18,77. Table is created, in which, when different values of the angle θ , are the values of n and calculated using formulas page 4 values of R_m(θ ), as well as the parameter, as a function of θ . From the condition of equality of values(θ ) calculated above the value of the right part of equation (4), we can obtain (using extrapolation graphic or otherwise) the desired value of R_mi.e. here(θ )≈ 18,77, where θ ≈ 53° , which corresponds to R_m≈0,073 M. Thus, for the parameter values chosen in this example, the received diameter of the pressure roller, which is D_m≈14,6 see

Increasing the load on the roller against specified above 1.5 times, R_m=6 kN, leads to the reduction calculated in this way the diameter of the pressure roller to the level of D_m≈11 see

If the design of the test bench based on the principle of unidirectional movement of the rollers along the rail, the trajectory of their rolling at the same speed is what I long enough (up to 1 m or more); during the test produce observations of surface States experienced head rail in the area of this path. Testing is carried out before the appearance on the surface of the rail contact fatigue defects 11.2 (classification of rail defects NTD/CPU-1-93). In each trial is recorded the number of cycles of the passage of the pressure roller along the rail, which is the value to compare the resistance of rails manufactured, for example, of different chemical composition or heat treatment of steels, to the emergence of contact fatigue defects.

Implementation of the proposed method when using the stand structures with reversible principle of the movement is explained by using the drawings, in which figure 1 shows a variant of the circuit of the test device, and figure 2 shows the section a-a figure 1.

On the surface of experienced rail 1, resting on the base 2, carry out the movement of the pressure rollers 3, simulating the impact of a railway wheel and a flange on the upper and side surfaces of the head, characteristic of contact of wheel and rail in curved track sections. The movement of the pressure rollers is reversible character driven via the shaft 4 from the flywheel 5, driven in rotation by electric motor 6 and the gear (gear box changes speeds) 7, and the force of the pressure roller is in the surface of the rail pass from the loading device 8 via the push beam 9 and the guide rollers 10. Thus, the influence of the pressure rollers on the test surface of the rail head 1 is cyclically repeated until the occurrence of contact fatigue defects Tina 11.2. The design of the mechanical assemblies of the test device, functionally linking all push 3, guide rollers 10 and the hinged connection with the rod 4, and the frame structure of a loading device 8 allows to vary the places of contact of the pressure rollers with the surface of the test specimen, including, remove the force of the pressure rollers on the side surface of the head (on the scheme conditionally not shown).

The proposed method allows to compare the resistance of rails, made for example of steel, which differ in chemical composition, or subjected to different heat treatment, the occurrence of contact fatigue defects. This mapping is performed at the preset speed mode (that is, at the same rotation speed of the flywheel), forces of the pressure rollers and the conditions of their contact with the sample surface. If necessary, assess the impact of dynamic parameters of interaction of a pair of “wheel - rail” in a broader range of their changes in resistance of the rail contact fatigue fracture in addition to the above samples for each series (with nl is scimi source characteristics) carry out tests in different speed modes, asking each test, in addition to rolling velocity, also defined the value of the load R and the place of contact of the pressure rollers with the surface of the sample. Conducting a series of tests with different set of loads on the pressure roller will allow you to build the dependence of the amplitude of the voltage from the number of cycles to failure that will significantly expand the scope of application of test results. For example, after verification of data on the development of contact fatigue in the rail head obtained by this method by comparing with the results of relevant experiments on the ring, the proposed method can be used for the purposes of quantitative forecasting service durability of rails.

When implementing the method based on the reverse principle of the rolling pressure of the rollers on the rail is actually happening with the changing speed (in the range from 0, at the pivot point, to a certain speed limit in the center defined by the set rotation speed of the flywheel). Thus, the occurrence of defects such 11.2 on the surface of the rail head with this test it is easy to determine the speed of the rolling rollers 3, in which they have arisen, if we use the formula

(where x is the coordinate of the defect measured from the Central the Noah trajectory point of rolling; ω - the angular velocity of the rotation of the flywheel; x_max- half-length of the trajectory of the rolling - corresponds to the coordinate of the turning point). However, despite the variable speed rolling, first, its value at the Central long trajectory rolling differs little from the maximum (largest radius of the flywheel), and, secondly, and in a reverse version of the schema tests there are a number of key opportunities to ensure similarity from the point of view of the developing vibration process in the cross-section of the rail sample for almost the entire length of the trajectory rolling. To this end, for example, it is possible to provide in a construction of a loading device 8 (and possibly pressure beam 9) the corresponding load reduction P_mwhen removing the roller from the center of the trajectory (this should be linked with additional vertical positive and negative efforts transmitted by the rod 4 from the flywheel 5), which provides additional opportunities to more fully assess the effect of velocity factor on the test result.

When testing new rails axisymmetric impact of the pressure roller will be carried out on the surface of the head of radius 0.5 m (e.g., rails R65), then with the same force and geometrical parameters used in the example above, in the execution of the method (ν =120 km/h, ν_m=4 m/s, P_m=4 kN), we obtain a value of R_m≈0,085 m If at the same time to increase the simulated speeds of up to ν =140 km/h, the radius of the pressure roller is required to be reduced to R_m≈0,064 m (D_m≈12,8 cm). From the above comparative assessments, it follows that a reasonable choice of speed in the process of testing largely can be attributed to the discretion of the designers of the test bench, subject to the requirements of the adequacy of the level of force on the pressure roller.

Use to simulate the impact of the moving wheels of the pressure rollers with a diameter of 32-34 mm at a wheel load of 100 N was allowed in experiments on the rail R65, starting with the rolling velocities of 1.5-2 m/s, to obtain the development of the vibrating process in the cross-section of the rail with a significant contribution of frequencies of about 10 kHz.

The frequency characteristics of the vibration process, developing cross-section of the rail, when tested in this way will be a much greater extent correspond to the frequency characteristics of the vibration occurring in the transverse cross section of the rail track conditions at speeds of rolling stock, simulated in the tests, including speeds higher compared with the method, taken as a prototype. This explanation is to be used in this way as samples rails of full size while reducing their size, as a complete waiver of compliance form, significantly limits the principal's ability to play in a test mode of the above-noted features of vibrating processes inherent in operating conditions with the specified speeds. Since the damping of these oscillations is very small, even with these small loads on the wheel can be dangerous factor rarely considered in traditional approaches to test the quality of rails), dramatically enhancing the rigidity of the dynamic effects on the material. This factor is a significant increase in the actual number of loading cycles, which is subjected to the rail material in the surface area of the head in comparison with the known types of tests, resulting in lower resistance steel rail contact fatigue failure.

Literature

1. Kislik VA and Karmazin A.I. assessment Method contact strength rail steel // Zavodskaya laboratoriya, 1964, No. 12. - C-1499.

2. Grdina J.V., Kotov, A.V. Artificial reproduction of the defect contact fatigue in samples cut from the rail head, " Izv. higher education institutions. Ferrous metallurgy, 1965, No. 6. - P.148-150.

3. Melentiev, L.P. ON some peculiarities of interaction of way and rolling stock while increasing the speed of the movement is of trains / Works VNIIZHT, WIP “Work train tracks when handling freight trains with speed of 90-100 km/h. - M.: Transport, 1979. - Pp.33-38.

4. Teodorovich D.B, fists S.M., Ants CENTURIES of Active technical system on the basis of materials and structures to managed properties, Izv. higher education institutions. Ferrous metallurgy, 2001, No. 2. - P.63-68.

5. Teodorovich D.B, an owl. The role of dynamic factor in quality testing of rails // Actual problems of production rails / Ed. by V.E. Gromov. - Novokuznetsk: Novokuznetsk, 2001. - S-146.

6. Belyaev NM resist materials. - M.: Fizmatgiz, 1962. - C.152-157.

7. Shounens G.M. Railway journey: the Textbook for high schools W.-D. transp. - M.: Transport, 1987. - 479 C.

The method of testing of rails on contact fatigue, which consists in the fact that the samples rail steel running pressure rollers in the longitudinal direction until the surface of the sample fishermen, as well as a deep indentation depth, as per, characterized in that the quality of samples used by the experienced rails, and the diameter of the pressure roller is chosen from the condition of equality of the reduction ratio of the linear size of the area of contact of the roller with a rail on the axis of the latter compared with the corresponding size that meets the operating conditions, and the reduction ratio of the speed of rolling of the roller relative to the MSE of the spine of the wheel rolling on the rail in operation.